Who is the other Caesar that Octavius mentions in Julius Caesar?

In Act 5, Scene 1, Antony and Octavius are holding a parley with Brutus and Cassius before the impending battle at Philippi. The young, hot-headed Octavius draws his sword and says:

Look, I draw a sword against conspirators.

When think you that the sword goes up again?

Never till Caesar's three and thirty wounds

Be well avenged, or till another Caesar

Have added slaughter to the swords of traitors.

Octavius is referring to himself. He is now Octavius Caesar as the heir to Julius Caesar. He is saying that he will not relinquish his sword unless he is slaughtered by the swords of traitors--i.e., Brutus and Cassius--who slaughtered his uncle Julius Caesar. He seems anxious to assert himself, since he is conscious that he is the youngest man present at the parley and by far the least experienced in battle.

Brutus immediately addresses Octavius as Caesar, showing he well understands that Octavius is referring to himself: